(1) Field of the Invention
The present invention relates to a light source unit and a projector having the light source unit, and more specifically, to a technique for an adjustment of light axes between a high pressure discharge lamp and a concave lens set in the light source unit.
(2) Description of the Related Art
High pressure discharge lamps as typified by high pressure mercury lamps have excellent properties such as high luminance, light emission effectiveness, and longevity. Thus, the high pressure discharge lamps are desirable as a Video Projector System (VPS) lamp for a light source unit of a projector. An example of the high pressure discharge lamps is disclosed in Japanese Laid-Open Patent Application No. 2001-101923.
In the projector, it is common that parallel light from the high pressure discharge lamp is used to display an image. In recent years, however, light source units, in which the light from the high pressure discharge lamp is converged and then used to display an image, have been introduced. According to this kind of light source units, a concave lens held by a holder is set in front of an ellipsoidal mirror (paraboloidal mirror) that surrounds the high pressure discharge lamp, and light axes of the ellipsoidal mirror and the concave lens are adjusted to be set at substantially the same position.
By adopting the light source unit having the above structure, it is possible to obtain various advantages. Specifically, in addition to a dramatic improvement in light utilization using the light from the high pressure discharge lamp collimated by the ellipsoidal mirror and converged by the concave lens, it is also possible to downsize optical elements on an optical path with the converging of the light.
At the same time, adopting the above light source unit, in which the light from the high pressure discharge lamp is converged by the concave lens, also has a disadvantage that the adjustment of the light axes in the light source unit becomes more strict than before.
In a case of the light source unit in which the parallel light is used, the light utilization is not affected much, even if positions of the light axes of the lamp and the optical device do not coincide. However, in a case in which the light from the high pressure discharge lamp is converged by the concave lens, if the light axes of the ellipsoidal mirror and the concave lens do not substantially coincide, a convergence point of the ellipsoidal mirror deviates from the concave lens. As a result, it becomes extremely hard to catch the light within the concave lens, and therefore, the light utilization decreases drastically.
Even though a rough positioning is done in a case of the light source unit in which the ellipsoidal mirror and the concave lens are used, the positioning is based on relative positions of a rim of a flange of the ellipsoidal mirror and a holder that holds the concave lens. With such a positioning method, the concave lens easily moves its position inside the rim of the flange, and accordingly, it becomes difficult to adjust the light axes to be set at a desirable position that is sufficient for the light source unit in which the light from the high pressure discharge lamp is converged by the concave lens.
The above noted problem in the positioning of the ellipsoidal mirror and the concave lens leads to decreased performance of the projector that uses the high pressure discharge lamp, and is desired to be solved as soon as possible. The same kind of problem occurs in a case in which an optical element such as a lens other than the concave lens is utilized.
Thus, a room for improvement is still left in order for a more strict adjustment of the light axes between the ellipsoidal mirror and the concave lens in the light source unit utilizing the high pressure discharge lamp.